1. Field of the Invention
The present invention relates to a reactor comprising a bundle of catalyst tubes, through whose space surrounding the catalyst tubes a heat exchange medium is passed, a pump for circulating the heat exchange medium for a reactor and a use.
2. Discussion of the Background
The conventional design of reactors of the generic type consists of a generally cylindrical container in which a bundle, i.e. a plurality of catalyst tubes is accommodated in a usually vertical arrangement. These catalyst tubes, which, if required, may contain supported catalysts, are tightly fastened at their ends in tube sheets and open in each case into a hood connected at the upper or lower end to the container. The reaction mixture flowing through the catalyst tubes is fed in and removed, respectively, via these hoods. A heat exchange medium circulation is passed through the space surrounding the catalyst tubes, in order to compensate the heat balance, in particular in the case of reactions involving considerable heat of reaction.
For economic reasons, reactors having a very large number of catalyst tubes are used, the number of catalyst tubes accommodated frequently being from 5 000 to 50 000.
Regarding the heat exchange medium circulation, it is known that a substantially homogeneous temperature distribution of the heat exchange medium is desirable in each horizontal section of the reactor, in order as far as possible to involve all catalyst tubes uniformly in the reaction. The supply of heat or removal of heat via external ring lines mounted in each case at the reactor ends and having a plurality of jacket orifices, as described, for example, in DE-B-34 09 159, serves for smoothing the temperature distribution.
It is known that reactors comprising a catalyst tube bundle are advantageously operated by the cocurrent procedure, both reaction mixture and heat exchange medium preferably being fed in at the upper reactor end and being removed from the lower reactor end.
With the countercurrent procedure, cocurrent flow has advantages such as higher throughputs, lower catalyst hotspot temperatures, desired increase in the heat exchange medium temperature in the direction of the final reaction in the catalyst tubes, good temperature uniformity of the heat exchange medium over the reactor cross section, i.e. good horizontal temperature stratification, clearly defined operating states over the height of the catalyst tube space owing to the lack of feedback by the heat exchange medium.
Axial-flow pumps, in particular propeller pumps, which have a vertical pump shaft, and which are mounted and driven at their upper end and thus usually transport the heat exchange medium downward have usually been used to date for circulating the heat exchange medium through the space surrounding the catalyst tubes. A pump arrangement having a vertical pump shaft which is mounted and driven at its lower end has not been realized technically to date, in particular owing to the complicated pump shaft packing required in this case.
DE-A 198 36 792.9 describes a reactor comprising cocurrent flow of reaction mixture and heat exchange medium in a proven arrangement of the pump, having a vertical pump shaft which is mounted and driven at its upper end, and which transports the heat exchange medium downward, where, by arranging a cylindrical partition in each case in the upper and the lower ring line and by using the space between upper and lower ring line for deflecting the heat exchange medium stream, the heat exchange medium of the outer lower ring line is fed, via a region in the space between lower and upper ring line, to the inner upper ring line, and via its jacket orifices to the space surrounding the catalyst tubes, and is removed via jacket orifices into the inner lower ring line and then via a space in the region between lower and upper ring line via the outer upper ring line. This provides a design solution which, with proven transport of the heat exchange medium downward by the pump, ensures flow around the catalyst tubes by the heat exchange medium downward and hence cocurrently with the reaction mixture likewise fed downward through the catalyst tubes. However, this solution requires a reactor adaptation which is complicated in design, in particular a corresponding division of upper and lower ring line and of the space between upper and lower ring line into a plurality of chambers.